<!DOCTYPE html>
<style>
  ::-webkit-scrollbar { background-color: red; }
  ::-webkit-scrollbar-track:hover { background-color: green; }
</style>
For manual test, move mouse over the red bar.
The test passes if the bar turns green on mouse over and red on mouse out.
<div style="width: 200px; height: 200px; overflow-y: scroll" id="scroller">
  <div style="height: 500px"></div>
</div>
<script src="../../../resources/run-after-layout-and-paint.js"></script>
<script>
if (window.eventSender) {
  runAfterLayoutAndPaint(function() {
    eventSender.mouseMoveTo(200, 100);
  }, true);
}
</script>
